One type of internal combustion engines typically employ a number of cylinders which compress a fuel and air mixture such that upon firing of a spark plug associated with each cylinder, the compressed mixture ignites. The expanding combustion gases resulting therefrom move a piston within the cylinder. Upon reaching an end of its travel in one direction within the cylinder, the piston reverses direction to compress another volume of the fuel and air mixture. The resulting mechanical kinetic energy can be converted for use in a variety of applications, such as, propelling a vehicle or generating electricity, for example.
Another type of internal combustion engine, known as a compression ignition engine, uses a highly-compressed gas (e.g., air) to ignite a spray of fuel released into a cylinder during a compression stroke. In such an engine, the air is compressed to such a level as to achieve auto-ignition of the fuel upon contact between the air and fuel. The chemical properties of diesel fuel are particularly well suited to such auto-ignition.
The concept of auto-ignition is not limited to diesel engines, however, and has been employed in other types of internal combustion engines as well. For example, a self-igniting reciprocating internal combustion engine can be configured to compress fuel in a main combustion chamber via a reciprocating piston. In order to facilitate starting, each main combustion chamber is associated with a prechamber, particularly useful in starting cold temperature engines. Fuel is injected into not only the main combustion chamber, but also the combustion chamber of the prechamber, as well, such that upon compression by the piston, a fuel and air mixture is compressed in both chambers. A glow plug or other type of heater is disposed within the prechamber to elevate the temperature therein sufficiently to ignite the compressed mixture. The combustion gases resulting from the ignition in the prechamber are then communicated to the main combustion chamber.
Other types of internal combustion engines use natural gas as the fuel source and include at least one piston reciprocating within a respective cylinder. A spark plug is positioned within a cylinder head associated with each cylinder and is fired on a timing circuit such that upon the piston reaching the end of its compression stroke, the spark plug is fired to thereby ignite the compressed mixture.
In still further types of internal combustion engines, prechambers are employed in conjunction with natural gas engines. Given the extremely high temperatures required for auto-ignition with natural gas and air mixtures, glow plugs or other heat sources such as those employed in typical diesel engines, can be ineffective. Rather, a prechamber is associated with each cylinder of the natural gas engine and is provided with a spark plug to initiate combustion within the prechamber which can then be communicated to the main combustion chamber. Such a spark plug-ignited, natural gas engine prechamber is provided in, for example, the 3600 series natural gas engines commercially available from Caterpillar Inc. of Peoria, Ill.
The trend continues to operate these engines under lean-burn conditions. Lean burn refers to the burning of fuel with an excess of air in an internal combustion engine (i.e. lean fuel/air ratio). The excess of air in a lean burn engine combusts more of the fuel and emits fewer unwanted emissions. However, the lean fuel/air ratio can make it difficult to consistently achieve complete and thorough combustion within the main combustion chamber.
U.S. Pat. No. 6,854,439 is entitled, “Prechamber Combustion System,” and is directed to a combustion system, particularly for a larger type diesel engine, featuring a prechamber with a generally cup-shaped bottom tip portion facing the engine's main combustion chamber and with a central transfer passage substantially aligned with the centerline of the prechamber and a plurality of additional transfer passages circumferentially arranged about the centerline of the prechamber. The combustion system uses a piston with a deep bowl formed in the piston crown into which the central transfer passage directs a strong direct charge of products of combustion from the prechamber.
There is a continued need in the art to provide additional solutions to enhance combustion in a prechamber to improve efficiency. For example, there is a continued need to enhance combustion in a prechamber by enhancing mixing within a prechamber.
It will be appreciated that this background description has been created by the inventors to aid the reader, and is not to be taken as an indication that any of the indicated problems were themselves appreciated in the art. While the described principles can, in some respects and embodiments, alleviate the problems inherent in other systems, it will be appreciated that the scope of the protected innovation is defined by the attached claims, and not by the ability of any disclosed feature to solve any specific problem noted herein.